Amplification of electric oscillations



Dec. 8, 1931. c. T. JACOBS AMPLIFICATION OF ELECTRIC OSCILLATIONS FiledSept. 27, 1950 .lllllll INVENTOR. Cime, 7." @www BY mi.

MLM

ATTORNEY Patented Dec. 8, 1931 ears stra CHARLES T. JZLCLCOPS,V OFCHATHAIV, NEWJ'ERSEY, ASSIGNOR TO THOMAS A. EDISON, INCORPORATED, OFWEST ORANGE, NEW JERSEY, A CORPORATIQE' OF NEW JERSEY AMPLIFICATION OFELCTRIG OSCLLATIONS Application filed September 27, 1930.

This invention relates to amplifying stages of, land similar to the typecommonly known as push-pull stages and more particularly to theelimination or minimization of objectionable hum or ripple components inthe output of such stages resulting from the excitation by alterna-tingcurrent of the filaments of any tubes employed therein. The inventionrelates specically to such stages wherein are employed tubes whosefilaments comprise their cathodes; and all tubes hereinafter referred toare intended to be considered as of that type, in distinction to thoseemploying indirectly heated cathodes.

In the use of any stage of amplification, it is necessary to connect theinput circuit return, or one side of the input circuit, to the filamentsystem of the tube or tubes employed; and it is the object of myinvention to provide a novel method of connection and adjustment of suchinput circuit return in a stage having a push-pull input circuit andemploying` a tube or tubes whose filaments are energized by alternatingcurrent,characterized by simplicity as well as great effectiveness inthe minimization of hum or ripple components in the output of such stageresultinO' from such alternating current excitation.

tfn the detailed description of my invent-ion hereinafter set forth,reference is had to the accompanying drawings, 0f which:

Figure 1 is a diagrammatic view of my invention in one form; and

Figure 2 is a like view thereof in a modified form.

When the filament of a tube is energized by alternating current it iscustomary to make connection of the input circuit return to a point ofintermediate potential with respect to the ends of the filament. If thelilamentand the extremities of the active portion thereof berespectively symmetrical about the axis of a helical grid, which is acommon tube construction, and if the filament be of generally uniformcharacteristicsthroughout its active length, such connection mayadvantageously be made to a point of exact midpotential with respect tothe ends of the active portion of the filament. Such point of connectionmight thenbe termed the opti- Serial No. 484,723.

mum point, in that connection thereto will reduce to a minimum hum orripple components in the output of the tube produced by the effect ofthe alternating current filament energization on the grid and anodepotentials applied to the tube, and in particular on such gridpotential. Failure of the tube construction or of the filamentcharacteristics to conform to the conditions outlined above may,however, cause the optimum point as defined above to be of other thanexact mid-potenti al with respect to the ends of the filament. Suchnon-coincidence of the optimum point and the mid-potential point is verycommon, even in tubes of the symmetrical lament construction outlinedabove, due to non-uniform characteristics of the filament over itsactive length.

The principal eect of a connection of the input circuit return' to apoint other than the optimum point therefor is that of the-applicationto the grid of the tube of an A. C voltage, cyclic with respect to thefilament energizing voltage and of amplitude equal to the potentialdifference between the point of actual connection and the optimum point.It is common practice to make possible connection of the input circuitreturn to the optimum point for any tube which may be used in a singletube stage by shunting across the filament terminals of the tube socketa potentiometer, and connecting the input circuit return to the variablecontact thereof. For any given tube, adjustment of said variable Contactto the optimum point of potential may beeffected by observing forminimum ripple in the ouput of the tube.

This method of obtaining optimum connection of the input circuit returnmay be applied to a stage employing two tubes or groups of tubes and soarranged that the dynamic grid potentials of one tube or group of tubesis opposite in phase to that of the other tube or group of tubes,'suchas the usual push-pull amplifying stage. Such application requires theuse of separate means for the energization of the lament or filaments ofeach of the'two tubes or groups of tubes from the same original sourceof alternation current, and two potentiometers each with a variablecontact, one shunted across the terminals of each such filament orfilaments. The separate filament energizing means may be two secondarywindings on the same transformer, two separate transformers whoseprimaries are supplied from the saine A. C. line, or the like.

I have discovered that in such a stage the arrangement outlined in thepreceding paragraph is needlesslycomplicated, both in coinposition andemployment, and in the stead thereof I employ such separate means forthe eneroization of the filament or filaments of each of the two tubesor groups of tubes, a single potentiometer, with variable Contact,shunted across the fila-ment terminals of one of the two tubes or groupsof tubes, and a fixed point of connection of intermediate potential withrespect to the filament terminals or extremities of the other tube orgroup of tubes. The variable contact of said potentiometer is connect-edto said lined point of connection and thereto is connected the inputcircuit return. Such fixed point of connection may be a fixed contact ortap on a resistance shunt-ed across the filament terminals of thelatter-mentioned tube or group of tubes; it may bea fixed tap on thetransformer secondary winding which may be employed for the energizationof the filament or filaments of such latter-mentioned tube or group oftubes or it may be made in any other suitable manner. In operation it isnecessary merely to adjust the variable contact of the singlepotentiometer until minimum ripple is observed in the output of thestage, as by auditory observation of the loud speaker if such is beingsupplied with energy from the stage.

In Figure l I show such a. stage incorporating my invention. TransformerT1 is shown as coupling the source of oscillations to be amplified bythe stage to the tubes Vl and V2 of the stage, these tubes havingcathodes or filaments Fl and F2, grids Gl and G2, and anodes A1 and A2,respectively. Transformer T2, with primary P, is shown as coupling thedynamic output of the stage to a loud speaker, for which, however, maybe substituted any other apparatus into which the stage is intended tofeed. Sources B and C, of D. C. anode and grid potential, respectively,for tubes Vl and V2 are shown by way of example as batteries. FilamentsFl and F2 are energized separately from seoondaries S1 and S2,respectively, of transformer T3, the primary of which is supplied withalternat-ing current by generator H, which is intended to depict anysuitable source of alternating current. Across Fl is connectedpotentiometer N, having variable contact S; and across F2 is connectedresistance R, having fixed tap V, located preferably at or near W thecenter of the resistance of R. S and V are connected together and to thesources B and C of D. C. potentials.

In Figure 2 I show a. similar stage, this i figure differing from Figurel in three respects: first, that resistance It with its tap V has beenreplaced by a tap IV on the secondary winding S2; secondly, that a groupof tubes, V1 and Vll, with all elements thereof respectively inparallel, have been substituted for the single tube Vl of Figure l and agroup, V2- alnd V22, for the single tube V2; and thirdly, that thebatteries B and C of Figure l have been replaced by a common battery orsource of direct current E and by resistance D, for self-biasing of thetubes, as will be understood. Other symbols have similar significancesto similar symbols in Figure l. It will be understood that in the firstrespect of diiference from Figure l, Figure 2 shows my invention in amodified form; but that in the other respects of difference, Figure 2merely illustrates alternative arrangements possible with any embodimentof my invention.

The `method. of adjustment of the circuit Vof Figure l is the movementof the contact S to that position on potentiometer N which results inminimum rippleV in the output of the stage, or across the entire primaryP of transformer T2. The condition which` tends principally to beestablished by such adjustment is the application to the grid of thetube V1 of an A. C. voltage similar in potential and phase to that whichexists between tap V and the optimum point of input circuit returnconnection for tube V2, or in other words to that which is applied tothe grid of tube V2 by virtue of its fixed input circuit return. Sincethe stage is responsive in dynamic 0peration to out-of-phase potentialson the grids of the two tubes, the A.. C. voltages applied to the gridsof the tubes as abovementioned, being in phase with each other, mutuallycancelV in their effect on the dynamic output, or in the voltageappearing across the entire primary P. When two or more paralleled tubesare used in each half of the stage, as in Figure 2, the method ofadjustment and theory of operation are identical with those applying inthe case of the use of single tubes in each half, as in Figure l. It maybe observed that a group of paralleled tubes tends to have a` singleeffective optimum point ofv input circuit return connection, as has asingle tube.

There are secondary factors which may cm for such a setting of contact Sthat the A. C. grid potentials abovementioned, though in phase with eachother, are slightly different in amplitude. Among these are inequalitiesin amplification factors or plateimpedances of the two tubes or groupsof paralleled tubes inexact center-tapping of primary P; effect on anodepotential of non-coincidence of actual input circuit return point andoptimum its lit'

point, and the like. These factors are, in whole or large part,automatically taken care of in adj ustment of contact S for minimumripple volta-ge across primary P but in almost no case do they influencesuch adjustment in more than a very minor degree, the grid voltageconsiderations outlined above remaining the principal determinant of theproper position of contact S for any given tubes or groups of tubes.

If for special purposes the dynamic output circuit of either tube orgroup of tubes be reversed in connection, my invention may be used inform and manner of adjustment as disclosed above, but actually thecontact S 'of potentiometer N will be so adjusted that the A. C.voltages caused to appear at the two grids willbe out of phase withrespect to each other. Such and other modifications, it will beunderstood, may be made in the choice and disposition of components andin manner of adjustment and theoretical operation Without departing fromthe spirit or scope of my-invention, as hereinabove or in the appendedclaims disclosed.

I claim l. In a system for the amplification of electric oscillations,in combination, two vacuum tubes each having at least an anode, a grid,and a filament comprising a cathode an input circuit for simultaneouslysupplying oscillations to be amplified to each of said tubes, insubstantially equal amplitudes but in opposite phase, said input circuitincluding means for rendering the grids of said tubes negative withrespect to their filaments; a circuit connected to the output of saidtubes to receive oscillations therefrom; means for supplying anodecurrent to said tubes; separate means for energizing the filament ofeach of said tubes from a common source of alternating current; aconnection from said input circuit to a point of non-adjustableintermediate potential with respect to the extremities of the filamentof one of said tubes; and a connection from said input circuit to apoint the potential of which may be varied over at least a portion ofthe range of potential between the extremities of the filament of theother of said tubes.

2. In a system for the amplification of electric oscillations, incombination, two vacuum tubes each having at least an anode, a grid, anda filament comprising a cathode; an input circuit for simultaneouslysupplying oscillations to be amplified to each of said tubes, insubstantially equal amplitudes but in opposite phase, said input circuitincluding means for rendering the grids of said tubes negative withrespect to their filaments; a circuit connected to the output of saidtubes to receive oscillations therefrom; means for supplying anodecurrent to said tubes; separat-e means for energizing the filament ofeach of said tubes from a common source of alternating current; a fixedtap on said means for energizing the filament of one of said tubes; a.rpotentiometer comprising a resistance element shunted across theextremities of the filament of the other of said tubes and a contactwhose position on said resistance element may )e varied; and aconnection from said tap and said contact to said input circuit.

3. In a system for the amplification of electric oscillations, incombina-tion, two vacuum tubes each having at least an anode, a grid,and a filament comprising a cathode; an input circuit for simultaneouslysupplying oscillations to be amplified to each of said tubes, insubstantially equal amplitudes but in opposite phase, said input circuitincluding means for rendering the grids of said tubes negative withrespect to their filaments a circuit connected to the output of saidtubes to receive oscillations therefrom; means for supplying anodecurrent to said tubes; separate means for energizing the filament ofeach of said tubes from a common source of alternating current;resistance shunted across the extremities of the filament of one of saidtubes, said resist-ance comprising two resistance sections in series,with a fixed contact between said sections; aV potentiometer comprisinga resistance elementV shunted across the extremities of the filament ofthe other of said tubes and a contact whose position on said resistanceelement may be varier; and a connection from each of said contacts tosaid input circuit.

4. In a system for the amplification of electric oscillations, incombination, a plurality of vacuum tubes each having at least an anode,agrid, and a. filament comprising a cathode, said tubes being arranged intwo groups, similar elements of the tubes in each group being'connectedin parallel; an input circuit for simultaneously supplying oscillationsto be amplified to each of said groups of tubes, in substantially equalamplitudes but in opposite phase, said input circuit including means forrendering the grids of said tubesnegative with respect to theirfilaments; a circuit connected to the output of said tubes to receiveoscillations therefrom; means for supplying anode current to said tubes;separate means for energizing the filaments of each of said groups oftubes from a common source of alternating current; a connection ,fromsaid input circuit to a point of nonadjustable intermediate potentialwith iespect to the extremities of the filaments of one of said groupsof tubes; and a connection from said input circuit toa point thepotential of which may be varied over at least a portion of the range ofpotential between the extremities of the filaments of the other of saidgroups of tubes.

5. In'a system for the amplification ofv electric oscillations, incombination, a plurality of vacuum tubes eachl having at least an anode,a grid, and a filament comprising a cathode, said tubes being arrangedin tivo groups, similar elements of the tubes in each group beingconnected in parallel; an input Circuit for simultaneously supplyingoscillations to be amplified to each of said groups of tubes, insubstantially equal amplitudes but in opposite phase, said input circuitincluding means for rendering theY grids of said tubes negative Withrespect to their la- Y ments; a circuit connected to the output of saidtubes to receive oscillations therefrom means for supplying anodecurrent to said tubes; separate means for energizing the filaments ofeach of said groups of tubes from a common source of alternatingcurrent; a lined tap on said means for energizing the filaments of oneof said groups of tubes; a potentiometer comprising a resistance elementshunted across the extremities of the filaments of the other of saidgroups of tubes and a contact Whose position on said resistance elementmay be varied; and a connec tion from said tap and said contact to saidinput circuit.

6. In a system for the amplification of electric oscillations, incombination, a plurality of vacuum tubes each having at least an anode,a grid, anda filament comprising a cathode, said tubes being arranged intWo groups, similar elements of the tubes in each group being connectedin parallel; an input circuit for simultaneously supplying oscillationsto be amplified to each of said groups of tubes, in substantially equalamplitudes but in opposite phase, said input circuit includiny means forrendering the grids of said tubes negative with respect to theirfilaments; a circ-uit connected to the output of said tubes to receiveoscillations therefrom; means for supplying anode current to said tubes;separate means for energizing the laments of each of said groups oftubes from a common source of alternating Current; resistance shuntedacross the extremities of the filaments of one of said Groups of tubes,said resistance comprising two resistance sections in series, with afixed contact between said sections; a potentiometer comprising aresistance element shunted across the eX- tremities of the filaments ofthe other of said groups of tubes and a Contact Whose position on saidresistance element may be varied; and a connection from each of saidcontacts to said input circuit.

7. The method of minimizing ripple currents in the output of anamplifying stage having a push-pull input circuit and employing tWovacuum tubes Whose filaments comprise their cathodes and are energizedby alternating Current, Which consists in sepa` rately energizing eachof said filaments from a common source of alternating current; in

non-adjustably returning said input circuit i' to the filament system ofone of said tubes;

and in so maintaining the point of return of said input circuit to thefilament system of the otli'er'of said tubes as to cause said tubes toproduce substantially equal and opposite ripple currents in said output.

8. The method of minimizing ripple currents in the output of anamplifying stage having a push-pull input circuit and employing twogroups of paralleled vacuum tubes Whose filaments comprise theircathodes and are energized by alternating current, Which consists inseparately energizing the paralleled filaments of each of said groups oftubes from a common source of alternating current; in non-adjustablyreturning said input circuit to the filament system of one of saidgroups oi tubes; and in so maintaining the point of return of said inputcircuit tothe filament system of the other of said groups of tubes as tocause said groups of tubes to produce substantially equal and oppositeripple currents in said output.

This specification signed this 26th day of September, 1930.

CHARLES T. JACOBS.

